Ceramic heat exchange tubes are known for use in heat recuperators, heat exchange units for gas turbine cycles and other heat exchange uses. Such tubes in many uses are subjected to differential gas pressure between the inside system fluid and the outside atmospheric fluid. Joints between tubes and at interconnecting passageways are difficult to make leak tight particularly where extremely high temperatures are encountered in normal operation of the heat exchange elements. For example, when used in connection with forging furnaces, aligned heat exchange tubes in a recuperator could be subject to temperatures of from 1500.degree. to 2400.degree. F. or perhaps even higher. At such temperatures, seals made of conventional materials could disintegrate or distort. In at least one prior application where such ceramic heat exchange tubes are used, springs were used to compress the mating faces of the seals to yieldably urge them into resilient engagement with each other in order to form gas pressure resistant seals. Such spring seals are useful although in some cases it was determined that due to the elevated temperature in the vicinity of the springs, the springs lose their temper in time and must be replaced or reprocessed to maintain the needed force on the seals.